Methods for producing agglomerates of metal powders and articles incorporating the agglomerates

ABSTRACT

Processes for making rigid, binder free agglomerates of powdered metal are disclosed. The agglomerates have a low tap density. Articles that contain binder free agglomerates made from electrochemically active powder are also disclosed.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of U.S. patent application Ser. No.10/346,783, filed Jan. 17, 2003, and entitled “METHODS FOR PRODUCINGAGGLOMERATES OF METAL POWDERS AND ARTICLES INCORPORATING THEAGGLOMERATES.” The aforementioned related application is herebyincorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention generally relates to a process for producing agglomeratesof metal powders. More particularly, this invention is directed to aprocess for producing rigid, porous, binder free agglomerates of metalpowders. This invention is also directed to devices that include therigid, binder free agglomerates.

Fine metal powders are used in a wide variety of devices to enabledesirable chemical reactions. For example, catalysts are incorporated inthe catalytic converts of vehicles powered by combustion engines. Thecatalyst facilitates the conversion of potentially harmful fumes toenvironmentally acceptable gases or liquids. In another example, metalpowders are used to store gases, such as hydrogen, in a solid matrix tominimize the hazards associated with the storage and transport ofhydrogen as a compressed gas. Fine metal powders are also used inbatteries and fuel cells. Commercially available batteries, includingboth rechargeable and non-rechargeable batteries, are used to powerportable devices such as flashlights, cameras and tape recorders. Onechemical system used to produce rechargeable batteries incorporates afinely divided metal hydride in one of the electrodes. Another chemicalsystem, typically used to manufacture non-rechargeable batteries, alsoknown as primary batteries, uses an alkaline electrolyte, manganesedioxide as the active cathode material and zinc as the active anodematerial. The zinc is usually disposed within the central region of thebattery as part of a gel. Prior to incorporating the zinc into thebattery, the zinc is comminuted so that a quantity of zinc powder with amajority of particles ranging from 25 microns to 500 microns isobtained. The individual particles are suspended in the anode gel whichprevents settling of the zinc particles within the battery.

One of the long-standing objectives of battery manufacturers is toproduce batteries with the ability to power a device for longer andlonger periods of time. The need to improve the battery's performance isespecially acute in devices that require large currents. As disclosed inJP Kokai 57[1982]-182972, the high discharge characteristic of a batterycan be improved by incorporating 5-30 weight percent of the zinc asparticles with a particle size of 25 microns or smaller. Unfortunately,as the percentage of particles that are 25 microns or smaller increases,the viscosity of the anode may become too high to process in high speedmanufacturing machines. One way to overcome this problem is to processall of the zinc particles into a single porous body. For example, U.S.Pat. No. 2,480,839 discloses an anode made of zinc powder or particlesthat have been compressed under sufficient pressure to agglomerate theparticles into a coherent body shaped as a hollow cylinder. In anotherexample, U.S. Pat. No. 3,645,793 describes cleaning the zinc powder witha mild acid and then pressing the zinc to form a porous structure. Thesepatents are directed to the production of coherent structures that aresuitable for use as an electrode in an electrochemical cell. All of theparticles are included in the compaction process and form a part of thecompacted electrode. Thus, these processes are not well suited for theproduction of electrodes that incorporate both agglomeratedelectrochemically active particles and non-agglomeratedelectrochemically active particles in the same electrode.

Other methods of handling the finely divided metal powders include thestep of utilizing an agglomerant to form the agglomerates. Theagglomerant may be a binder that acts as an adhesive to secure particlesto one another thereby enabling the formation of the agglomerates.Alternatively, the agglomerant may be a pore former which facilitatesthe formation of the agglomerate but is then removed from theagglomerate thereby forming pores within the agglomerate. Unfortunately,the use of an agglomerant may have a negative impact on the performanceof the agglomerated powder. For example, if a battery includes anelectrode that uses agglomerates of electrochemically active materialthat incorporate an organic binder, such as polyvinyl alcohol (PVA),then the particles are inherently coated with the electricallynonconductive PVA. The coating increases the internal resistance of theelectrode that includes the coated, agglomerated particles. As theelectrode's internal resistance increases, the battery's run timedecreases. Furthermore, there are potential problems associated with thecost of the binder as well as the volume of space occupied by thebinder. As the volume of space dedicated to the binder increases, thequantity of electrochemically active material must be decreased to makeroom for the binder. As the quantity of active material is decreased,the cell's run time is reduced.

Therefore, there exists a need for a process that produces small, rigid,binder free agglomerates that do not compromise the performance of theagglomerated particles. The process should not require the use of anadditive, such as a binder or pore former, to enable production of theagglomerates.

BRIEF SUMMARY OF THE INVENTION

The process of the present invention produces rigid, binder freeagglomerates that are appropriately sized for mixing withnon-agglomerated particles to produce a flowable mixture.

In one embodiment, this invention is a process that includes the stepsof providing an electrochemically active material in comminuted form andthen forming rigid, binder free agglomerates that consist essentially ofthe electrochemically active material.

In another embodiment, this invention is an electrochemical cell thatincludes an electrode that incorporates the rigid, binder freeagglomerates that consist essentially of the electrochemically activematerial.

In another embodiment, this invention is a hydrogen storage vessel thatincorporates the rigid, binder free agglomerates.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows steps in one embodiment of a process of this invention;

FIG. 2 is a cross section of an electrochemical cell of this inventionthat includes rigid, binder free agglomerates made by the process shownin FIG. 1;

FIG. 3 is a schematic drawing of a roll compactor and granulationprocess;

FIG. 4 shows a line chart of internal resistance data;

FIG. 5 shows a line chart of internal resistance data;

FIG. 6 shows a bar chart of cell service data;

FIG. 7 is a scanning electron micrograph of zinc powder agglomerates;

FIG. 8 is a scanning electron micrograph of zinc powder agglomerates;and

FIG. 9 is a scanning electron micrograph of zinc powder agglomerates.

DETAILED DESCRIPTION OF THE INVENTION

The following terms and phrases are defined for use herein.

The phrase “rigid, binder free agglomerate,” means an assemblage ofparticles which are rigidly joined together without the use of a binder.Therefore, each particle is physically secured to at least one otherparticle in the rigid, binder free agglomerate. Particles that are inclose proximity to one another but are not associated via a physicalconnection are not considered to form a rigid, binder free agglomerate.

The term “agglomerated particles” means two or more particles that forman agglomerate.

The term “non-agglomerated particles” means two or more particles thatare not physically associated with each other.

Referring now to the drawings and more particularly to FIG. 1, there isshown a chart of process steps including both required and optionalsteps. Step 10 involves providing a quantity of electrochemically activematerial in comminuted form. In a preferred embodiment, the activematerial is zinc powder that has been produced by air atomization orcentrifugal atomization of molten zinc. The majority of the zincparticles typically range in size from 25 microns to 500 microns. Instep 12, the particles may be sorted based on size, shape or some othercharacteristic before continuing with the processing of the comminutedpowder. In step 14, the comminuted powder is formed into porous, rigid,binder free agglomerates that consist essentially of theelectrochemically active material. Preferably the electrochemicallyactive material accounts for one hundred percent, by weight, of thebinder free, rigid agglomerates. However, due the existence ofimpurities in commercial manufacturing processes, minute amounts offoreign material may unintentionally become incorporated into some ofthe rigid, binder free agglomerates during the manufacturing process.Preferably the contaminants would account for less than one percent, byweight, of the rigid agglomerates. More preferably, the contaminantswould account for less than one-tenth of one percent, by weight, of therigid agglomerates. Most preferably, the contaminants would account forless than one-hundredth of one percent, by weight, of the rigidagglomerates.

The rigid, binder free agglomerates formed in step 14 may bemanufactured to the desired density and size by adjusting processparameters in a manufacturing process, such as, a compaction process, adirect fusing process or an induction heating process. However, if therigid agglomerates are larger than desired, they may be granulated, asrepresented by step 16, to reduce the size of the rigid agglomerates.Granulation may be accomplished, for example, in a machine thatincorporates blades and/or beater bars to fragment the original rigidagglomerates into smaller rigid agglomerates. If desired, the fracturedrigid agglomerates may then be sorted, as represented by step 18, togenerate rigid agglomerates having the desired size. The sorting may beaccomplished by sieving the agglomerates. The agglomerates may also beannealed as represented by step 20.

An electrochemically active material that is useful in a process of thisinvention is zinc or a zinc alloy that incorporates one or more of thefollowing elements: indium, bismuth, aluminum, magnesium or lead. Asuitable zinc alloy contains 100 ppm of bismuth, 200 ppm of indium and100 ppm of aluminum. Comminuted zinc alloys that are suitable for use inelectrochemical cells may be purchased from Umicore (Belgium), Noranda(Canada), Big River Zinc (United States) and Mitsui (Japan). Theparticles may be shaped as: flakes, as disclosed in U.S. Pat. No.6,022,639; spherical particles, as disclosed in U.S. Pat. No. 4,606,869;various other shapes as disclosed in WO 98/50,969; or irregularlyshaped.

As represented by step 12 in FIG. 1, prior to forming the porous, rigid,binder free agglomerates, the comminuted active material may beprocessed to isolate particles within a desirable size range. Ascreening process that uses a single mesh screen, such as a 200 meshscreen, is a suitable means for sorting the particles. Alternately, atwo mesh screen screening process may be used. For example, thecomminuted active material may be processed by selecting only thoseparticles that will flow through a 40 mesh screen but will not flowthrough a 325 mesh screen. The porosity of the rigid agglomerate can beinfluenced by selecting particles within a specified range. A preferredrange of particle sizes is 25 microns to 70 microns. A more preferredrange of particle sizes is 25 microns to 50 microns.

The step of forming rigid, binder free agglomerates from the comminutedelectrochemically active material can be accomplished using a variety ofmanufacturing processes. In a preferred embodiment, the step of formingthe agglomerates utilizes a compaction process. Suitable means forforming the comminuted material into rigid, binder free agglomeratesincludes a roll compactor or a high pressure extruder. In addition torelying upon pressure to form the particles into agglomerates, variousforms of energy may also be used with the pressure to cause theparticles to become agglomerated. For example, in addition to the use ofpressure, the particles may be made to directly fuse with one another bycontacting some of the particles with an ultrasonic welder therebycausing some of the particles to vibrate against adjoining particles.The vibration results in the generation of sufficient heat to causelocalized welding of particles to one another. Induction heating may beused instead of an ultrasonic welder to effect direct fusing of theparticles.

As represented by step 20 in FIG. 1, the agglomerates ofelectrochemically active material may be annealed. The annealing isaccomplished by heating the agglomerates to a temperature sufficient torelease the stress created in the agglomerate during the process used togenerate the agglomerates. For many comminuted metal powders, such aszinc, the agglomerated zinc must be heated to a temperature above 100°C. but well below the melting point of zinc. Preferably, the temperatureof the agglomerate would not exceed 200° C.

Referring to FIG. 3, forming of the agglomerates by compaction of theparticles can be accomplished by feeding a quantity of comminutedparticles into the gap between opposing rolls in roll compactor 30.Compactor 30 includes a powder storage hopper 32, a first screw conveyor34 which is a horizontal screw, a second screw conveyor 36 which is avertical screw, a first roller 38 and a second roller 40. First roller38 rotates in a clockwise direction, as indicated by arrow A, whilesecond roller 40 rotates in a counterclockwise direction, as indicatedby arrow B. Rollers 38 and 40 may be made of hardened steel. The gap(not shown) between rollers 38 and 40 is one of the variables that maybe adjusted to form agglomerates with the desired porosity. The surfaceof rollers 38 and 40 may be modified to increase the coefficient offriction between the roller and the comminuted material. In a preferredembodiment, the surface of both rollers is coated with a ceramic layerto improve the coefficient of friction between the rollers and the zincparticles. Alternatively, the surface of the rollers may be sand blastedto improve their ability to grip the comminuted material and force itthrough the gap between the rollers.

Located beneath roll compactor 30 is granulator 42 which includes screen46. As the comminuted powder 48 in hopper 32 is fed to and through thegap between rollers 38 and 40, the powder is formed into thinagglomerated strips 50 that are too long for use in an electrode of acylindrical AA alkaline electrochemical cell that measures approximately50 mm high and 14 mm in diameter. Strips 50 are made to collide withbeater bar assembly 44 which fragments the pellets into smaller rigidagglomerates 52. The openings in sieving screen 46 allow a portion ofthe fragmented rigid agglomerates to pass through the screen andaccumulate in catch basin 54. If desired, the accumulated agglomeratesmay be processed through additional granulation and screening machineryuntil rigid, binder free agglomerates within a desired size range areobtained. Preferably, the rigid, binder free agglomerates will passthrough a 40 mesh screen. If desired, the agglomerates that pass througha 325 mesh screen may be eliminated.

In addition to the size of the agglomerate, the tap density of therigid, binder free agglomerates is one of the characteristics that canbe used to identify agglomerates that are suitable for use inelectrochemical cells. Preferably, the tap density of the agglomeratesis less than 2.95 g/cc. More preferably, the tap density is less than2.85 g/cc. Even more preferably, the tap density is less than 2.60 g/cc.Most preferably, the tap density is less than 2.40 g/cc. Tap density ismeasured using the following procedure. First, dispense fifty grams ofthe binder free zinc agglomerates into a fifty milliliter graduatedcylinder. Second, secure the graduated cylinder containing the zincagglomerates onto a tap density analyzer such as a model AT-2 “Auto Tap”tap density analyzer made by Quanta Chrome Corp. of Boynton Beach, Fla.,U.S.A. Third, set the tap density analyzer to tap five hundred andtwenty times. Fourth, allow the tap density analyzer to run therebytapping the graduated cylinder by rapidly displacing the graduatedcylinder in the vertical direction five hundred and twenty times. Fifth,read the final volume of agglomerated zinc in the graduated cylinder.Sixth, determine the tap density of the agglomerates by dividing theweight of the agglomerates by the volume occupied by the agglomeratesafter tapping.

Compaction of comminuted electrochemically active material to formrigid, binder free agglomerates is a preferred manufacturing processbecause a large quantity of agglomerates can be generated quickly andinexpensively. Shown in FIG. 7 is a scanning electron micrograph (SEM)of agglomerated zinc particles. The agglomerates were produced using aroll compaction process that did not utilize additional energy inputduring the production process. Despite the compaction, the individualparticles of zinc are readily distinguishable components of theagglomerates. The agglomerates are highly porous structures that arecapable of storing a liquid, such as the electrolyte in anelectrochemical cell, within the agglomerate. The agglomerates wereformed without using a binder or pore former. Consequently, the surfacesof the particles are not coated and the voids between particles are notplugged with a binder that could inhibit the electrochemical performanceof the zinc particles.

Other processes, referred to herein as direct fusing processes, can alsobe used to produce rigid, binder free agglomerates. One fusing processuses ultrasonic energy to fuse particles of the electrochemically activematerial to one another until binder free, rigid agglomerates with thedesired tap density and size are obtained. Shown in FIG. 8 is an SEM ofzinc agglomerates formed using ultrasonic energy. The agglomerates wereformed without the use of a binder or other agglomerant. The size andshape of the individual particles are not distorted by the use ofultrasonic energy to fuse individual particles to one another. Theagglomerates are highly porous structures capable of trapping andretaining liquid within the pores of the agglomerate.

Shown in FIG. 9 is an SEM of zinc particles formed using both compactionand ultrasonic energy. The individual particles of zinc were compressedduring the compaction process thereby eliminating many of the voidsbetween the particles.

Referring now to FIG. 2, there is shown a cross-sectional view of anelectrochemical cell. Beginning with the exterior of the cell, thecell's components are the container 60, first electrode 62 positionedadjacent the interior surface of container 60, separator 64 contactingthe interior surface 66 of first electrode 62, second electrode 68disposed within the cavity defined by separator 64 and closure member 70which is secured to container 60. Container 60 has an open end 72, aclosed end 74 and a sidewall 76 therebetween. The closed end 74,sidewall 76 and closure member 70 define a volume in which the cell'selectrodes and electrolyte are housed. A quantity of electrolyte, suchas a thirty-seven percent by weight aqueous solution of potassiumhydroxide, is placed in contact with the first electrode 62, secondelectrode 68 and separator 64.

First electrode 62 includes manganese dioxide as the electrochemicallyactive material and an electrically conductive component, such asgraphite. Additives, such as Teflon® and polyethylene, may be added tothe flowable dry mixture of manganese dioxide and graphite. The mixtureis molded against the interior surface 78 of container 60 therebyforming a cylinder. Separator 64 is inserted into the cylinder definedby first electrode 62 thereby providing an electrically nonconductive,ionically permeable layer on the interior surface of first electrode 62.

Second electrode 68 includes an electrochemically active component, suchas zinc particles, a gelling agent and an aqueous based alkalineelectrolyte. A suitable gelling agent is a crosslinked polyacrylic acid,such as Carbopol 940®, which is available from Noveon of Cleveland,Ohio, U.S.A. Carboxymethylcellulose, polyacrylanide and sodiumpolyacrylate are examples of other gelling agents that are suitable foruse in an alkaline electrolyte solution. The aqueous based alkalineelectrolyte includes thirty-six percent, by weight, potassium hydroxide,three percent, by weight, zinc oxide, and three-tenths of one percent,by weight, sodium silicate. The remainder of the solution is water. Anaqueous based alkaline solution of 0.1 N potassium hydroxide isincorporated into the second electrode's manufacturing process. Otheradditives, such as organic and/or inorganic corrosion inhibitors, mayalso be included in the second electrode. Indium hydroxide is an exampleof a suitable inorganic corrosion inhibitor. The second electrode'scomponents are blended to form a flowable gel. The zinc particlestypically account for 63% to 72% by weight of the second electrode whichmay also be referred to herein as the anode.

Closure member 70 is secured to the open end of container 60 therebysealing the electrochemically active ingredients within the cell. Theclosure member includes a seal member 80 and a current collector 82. Inother embodiments, the seal body could be a ring shaped gasket. The sealmember includes a vent that will allow the seal member to rupture if thecell's internal pressure becomes excessive. The seal member may be madefrom Nylon 6,6 or another material, such as a metal, provided thecurrent collector is electrically insulated from the container whichserves as the current collector for the first electrode. Currentcollector 82 is an elongated nail shaped component made of brass. Thecollector is inserted through a centrally located hole in the sealmember.

To demonstrate the advantages made possible by the process of thisinvention, conventional zinc powder was processed according to thefollowing description and then used to manufacture electrochemicalcells. The cells were then characterized by discharging them on aservice test to determine the cells' run time. The internal resistanceof representative cells was also measured. The data shown in FIG. 4 andFIG. 5 provide evidence that the cells made with rigid, binder freeagglomerates of zinc in the cell's anode had a lower internal resistanceduring the discharge of the cells than did the comparable control cellswhich had an equivalent quantity of electrochemically active materialthat did not include any rigid, binder free agglomerates of zinc.Furthermore, as shown in FIG. 6, the cells comprising the rigid, binderfree, zinc agglomerates had significantly longer run times than did thecells with an equivalent quantity of electrochemically active materialthat did not include any rigid, binder free agglomerates of zinc.

In one trial, anodes for cells of the present invention were prepared asfollows. First, a quantity of zinc alloy, in particulate form, wasprovided. The zinc alloy included 100 ppm of bismuth, 200 ppm of indiumand 100 ppm of aluminum. The zinc powder was sieved by disposing theparticles on a mesh screen with multiple openings and then vibrating theparticles across the screen so that particles smaller than the openingswould pass through the screen and particles larger than openings wouldnot pass through the screen. The screen was constructed so that eachopening had the same dimensions as every other opening in the screen.The zinc powder was sieved so that the particles smaller than 70 micronsand larger than 25 microns were collected in a first portion of powder.Particles larger than 70 microns were collected in a second portion ofpowder. Only the first portion of powder was then fed through a rollmill compactor and granulator as depicted in FIG. 3. A suitable rollcompactor and granulator may be purchased from the Fitzpatrick Companyof Elmhurst, Illinois, U.S.A. In this trial, the compactor's rollerswere made from 316 stainless steel and had a roll surface finish, priorto the application of a ceramic coating, of 32-62 RA. The ceramiccoating had a thickness of 0.13 mm to 0.18 mm and a hardness of 72Rockwell C. The roller's speed was three revolutions per minute. Theroll pressure was 2,260 pounds per linear inch. The speed of thehorizontal screw was 16 RPM, and the speed of the vertical screw was 175RPM. The gap between the rollers was set at 0.254 mm.

After passing through the roll compactor, the comminuted particles wereformed into strips of agglomerated particles that were fed into agranulator that fractured the strip into smaller granules ofagglomerated particles. The speed of the granulator's rotor was 1000RPM. The opening in the granulator's screen was 1.27 mm. Theagglomerates that passed through the granulator's screen were thensorted using a 40 mesh, US standard, screen. The openings in a 40 meshscreen allow only agglomerates smaller than 420 microns to flow throughthe screen. The screening process generated a first distribution ofagglomerates that flowed through the 40 mesh screen and a seconddistribution of agglomerates that did not flow through the 40 meshscreen. The rigid, binder free agglomerates in the first distributionhad a tap density of 2.83 g/cc and the size of the agglomerates wasbetween 150 microns and 300 microns. The following anode mixes were thenprepared with only the first distribution of agglomerates. Thequantities of the anode components are in percent by weight.

Lot Number Anode Component 1 2 3 4 5 Zinc Agglomerated — 68.00 34.0017.00 8.50 Non-agglomerated 68.00 — 34.00 51.00 59.50 Gelling Agent 0.440.44 0.44 0.44 0.44 36% KOH Electrolyte 30.20 30.20 30.20 30.20 30.20w/ZnO and sodium silicate 0.1 N KOH 1.36 1.36 1.36 1.36 1.36 TOTAL100.00 100.00 100.00 100.00 100.00

AA size batteries were then made with each of the anode mixes. Withinall five lots, all of the cell components except for the anode mixeswere identical.

FIG. 6 shows the run times for cells from all five lots that weredischarged per the following test regime. Each cell was “pulse” testedby individually discharging the cell at a rate of one amp for sixtyseconds and then allowing the cell to rest for five seconds before thenext pulse was begun. Each “sixty seconds on/five seconds off” cycle wascounted as one pulse. The test was continued until the cell's closedcircuit voltage fell below a 0.9 volt cutoff. The number of pulses thateach cell provided before the cell's closed circuit voltage fell belowthe voltage cutoff was recorded. Shown in FIG. 6, in bar chart format,is the data collected from the pulse testings. Lot number one is the“control” lot that incorporated only non-agglomerated zinc particles inthe anode. The average number of pulses provided by the cells in lot onewas defined as 100% for the purpose of creating a numerical performancestandard against which the other lots could be normalized. The cells inlot number two contained only agglomerated zinc particles. In lot numberthree, one-half of the zinc, by weight, had been agglomerated and theother half had not been agglomerated. In lot number four, one-fourth ofthe zinc in each cell had been agglomerated and three-fourths wasnon-agglomerated. In lot number five, one-eighth of the zinc in eachcell had been agglomerated and seven-eighths of the zinc had not beenagglomerated. The data in FIG. 6 demonstrates that the electrochemicalcells, in which at least a portion of the zinc was agglomerated intorigid, binder free agglomerates, provided approximately 12% to 23% morerun time than comparable cells that contained only non-agglomeratedzinc. Furthermore, the cells that contained no more than one-half oftheir zinc in the form of rigid, binder free agglomerates provided moreservice than cells that contained all of their zinc in the form ofrigid, binder free agglomerates. Thus, the advantage of incorporatingrigid, binder free agglomerates of zinc into the anode of alkalineelectrochemical cells has been demonstrated.

In another trial, a quantity of comminuted zinc particles wasagglomerated in a process similar to the previously described processused to produce agglomerates for lots two through five, except that thesize of the agglomerates was limited to less than 825 microns but morethan 250 microns for lot six and less than 250 microns but more than 100microns for lot seven. Three lots of AA size cells were made in order tocharacterize the impact that incorporating rigid, binder freeagglomerates of zinc into the anode would have on the cell's internalresistance during discharge on the previously described sixty secondson/five seconds off, one amp constant current test. The anode formulasused to make the three lots of cells are shown below. The quantities ofthe anode components are in percent by weight.

Lot Number Anode Component 6 7 8 Zinc Agglomerated 70.00 35.00 —Agglomerate size 250-825 microns- 100-250 microns — Non-agglomerated —35.00 70.00 Gelling Agent 0.42 0.42 0.42 36% KOH Electrolyte 28.39 28.3928.39 with zinc oxide and sodium silicate Indium Hydroxide 0.02 0.020.02 0.1 N KOH 1.17 1.17 1.17 TOTAL 100.00 100.00 100.00

Within all three lots, all of the cells' components except for the anodemixes were identical.

Shown in FIG. 4 are two line graphs which show the changes in internalresistance when cells from lot 6, represented by line 90, and lot 8,represented by line 92, were discharged on the pulse test. The dataclearly shows that the cells in lot six, which incorporated only rigid,binder free agglomerates, had lower voltage drops during discharge thandid the comparable cells in lot eight that utilized onlynon-agglomerated zinc. The lower voltage drop is indicative of a lowerinternal resistance. As the cell's internal resistance decreases, thecell's run time will increase.

Shown in FIG. 5 are two line graphs which show the changes in internalresistance when cells from lot 7, represented by line 94, and lot 8,represented by line 96, were discharged on the pulse test. This dataclearly shows that cells in lot 7, which incorporated 50% by weightrigid, binder free zinc agglomerates and 50% by weight non-agglomeratedzinc, had lower voltage drops during discharge on the pulse test thandid the comparable cells in lot 8 that utilized only non-agglomeratedzinc.

The data in FIGS. 4, 5 and 6 demonstrate that including rigid, binderfree agglomerates of zinc in the anode of electrochemical cells improvescell performance by reducing the anode's internal resistance during thedischarge of the cell thereby allowing the cell's run time to beincreased.

The above description is considered that of the preferred embodimentsonly. Modifications of the invention will occur to those skilled in theart and to those who make or use the invention. Therefore, it isunderstood that the embodiments shown in the drawings and describedabove are merely for illustrative purposes and are not intended to limitthe scope of the invention, which is defined by the following claims asinterpreted according to the principles of patent law, including theDoctrine of Equivalents.

1. An electrochemical cell having an electrode comprising a plurality ofagglomerates, wherein the plurality of agglomerates are made by aprocess comprising the steps of: (a) providing an electrochemicallyactive material in comminuted form, wherein said electrochemicallyactive material consists essentially of at least one selected from thegroup consisting of: zinc and an alloy of zinc; and (b) forming aplurality of rigid, binder free agglomerates consisting essentially ofsaid electrochemically active material, wherein a tap density of saidagglomerates is less than 2.85 g/cc.
 2. The electrochemical cell ofclaim 1, wherein said electrode comprises non-agglomerated particles ofelectrochemically active material.
 3. The electrochemical cell of claim2, wherein said non-agglomerated particles of electrochemically activematerial comprises at least 50%, by weight, of a total quantity ofelectrochemically active material in said electrode.
 4. Theelectrochemical cell of claim 1, wherein said non-agglomerated particlescomprise particles shaped as flakes.
 5. The electrochemical cell ofclaim 1, wherein said agglomerates consist of said electrochemicallyactive material.
 6. The electrochemical cell of claim 1, wherein saidtap density of said agglomerates is less than 2.60 g/cc.
 7. Theelectrochemical cell of claim 1, wherein said tap density of saidagglomerates is less than 2.40 g/cc.
 8. The electrochemical cell ofclaim 1, wherein, prior to forming the agglomerates, said activematerial is limited to particles that will flow through a 40 mesh USstandard screen but will not flow through a 325 mesh US standard screen.9. The electrochemical cell of claim 1, wherein at least 95% by weightof said agglomerates will pass through a 40 mesh US standard screen andwill not pass through a 325 mesh US standard screen.
 10. Theelectrochemical cell of claim 1, wherein said forming step comprisescompacting said active material.
 11. The electrochemical cell of claim10, wherein said process further includes the step of granulating saidcompacted agglomerates thereby forming granulated agglomerates.
 12. Theelectrochemical cell of claim 11, wherein said process further includesthe step of selecting said granulated agglomerates that can flow througha 40 mesh US standard screen.
 13. The electrochemical cell of claim 1,wherein said forming step comprises the step of directly fusing saidcomminuted active material.
 14. The electrochemical cell of claim 13,wherein said step of directly fusing said comminuted active materialcomprises exposing said active material to ultrasonic vibrations. 15.The electrochemical cell of claim 1, wherein said process furtherincludes the step of annealing said rigid, binder free agglomerates. 16.The electrochemical cell of claim 15, wherein said annealing stepcomprises heating said agglomerates above 100° C. but below meltingpoints of said active material.
 17. The electrochemical cell of claim 1,wherein said alloy of zinc comprises at least one element selected fromthe group consisting of bismuth, indium, magnesium and aluminum.
 18. Anelectrochemical cell containing an electrode comprising a plurality ofrigid, binder free agglomerates of an electrochemically active material,wherein said electrochemically active material consists essentially ofat least one selected from the group consisting of: zinc and an alloy ofzinc, and wherein a tap density of said agglomerates is less than 2.85g/cc.
 19. The electrochemical cell of claim 18, wherein saidagglomerates consist of said electrochemically active material.
 20. Anelectrochemical cell having an electrode comprising a plurality ofagglomerates, wherein the plurality of agglomerates are made by aprocess comprising the steps of: (a) providing an electrochemicallyactive material in comminuted form, wherein said electrochemicallyactive material consists essentially of at least one selected from thegroup consisting of: zinc and an alloy of zinc; and (b) forming aplurality of rigid, binder free agglomerates consisting essentially ofsaid electrochemically active material, wherein said agglomerates flowthrough a 420 micrometer opening size (40 mesh) screen.
 21. Theelectrochemical cell of claim 20, wherein a tap density of saidagglomerates is less than 2.85 g/cc.
 22. The electrochemical cell ofclaim 20, wherein said active material is limited to particles that willnot flow through a 325 mesh US standard screen.
 23. The electrochemicalcell of claim 20, wherein said agglomerates have a particle size in therange of 25-70 microns.
 24. The electrochemical cell of claim 20,wherein said forming step comprises compacting said active material. 25.The electrochemical cell of claim 20, wherein said process furtherincludes the step of granulating said compacted agglomerates therebyforming granulated agglomerates.
 26. The electrochemical cell of claim20, wherein said process further includes the step of selecting saidgranulated agglomerates that can flow through a 40 mesh US standardscreen.
 27. The electrochemical cell of claim 20, wherein said formingstep comprises the step of directly fusing the comminuted activematerial.
 28. The electrochemical cell of claim 27, wherein said step ofdirectly fusing the comminuted active material comprises exposing saidactive material to ultrasonic vibrations.
 29. The electrochemical cellof claim 20, wherein said process further includes the step of annealingsaid rigid, binder free agglomerates.
 30. The electrochemical cell ofclaim 20, wherein said alloy of zinc comprises at least one elementselected from the group consisting of bismuth, indium, magnesium andaluminum.
 31. An electrochemical cell containing an electrode comprisinga plurality of rigid, binder free agglomerates of an electrochemicallyactive material, wherein said electrochemically active material consistsessentially of at least one selected from the group consisting of: zincand an alloy of zinc, and wherein said agglomerates flow through a 420micrometer opening size (40 mesh) screen.
 32. The electrochemical cellof claim 31, wherein said agglomerates consist of said electrochemicallyactive material.